Microelectronic packages having stacked accelerometer and magnetometer die and methods for the production thereof

ABSTRACT

Methods for fabricating multi-sensor microelectronic packages and multi-sensor microelectronic packages are provided. In one embodiment, the method includes positioning a magnetometer wafer comprised of an array of non-singulated magnetometer die over an accelerometer wafer comprised of an array of non-singulated accelerometer die. The magnetometer wafer is bonded to the accelerometer wafer to produce a bonded wafer stack. The bonded wafer stack is then singulated to yield a plurality of multi-sensor microelectronic packages each including a singulated magnetometer die bonded to a singulated accelerometer die.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of co-pending U.S. application Ser. No.14/197,962, filed Mar. 5, 2014.

TECHNICAL FIELD

Embodiments of the present invention relate generally to microelectronicpackaging and, more particularly, to microelectronic packages includingstacked accelerometer and magnetometer die, as well as to methods forthe fabrication thereof.

BACKGROUND

Microelectronic packages are now commonly produced to contain two ormore multi-axis sensors. For example, a microelectronic package mayinclude a three axis accelerometer and a three axis magnetometercontained within a molded package body. The magnetometer may be a solidstate device, which is produced on a first semiconductor substrate ordie (referred to herein as a “magnetometer die”). By comparison, theaccelerometer may be a Microelectromechanical Systems (MEMS) device,which is formed on a second semiconductor substrate or die (referred toherein as an “accelerometer die”). During fabrication of the package, aseparate die or cap piece may be bonded over the accelerometer die toenclose the MEMS transducer structure within a hermetically-sealedcavity to optimize performance of the accelerometer. After bonding ofthe cap piece, a pick-and-place tool may be utilized to position themagnetometer die over the cap piece. The magnetometer and accelerometerdie may then be interconnected and overmolded or otherwise encapsulatedwithin a dielectric material. Depending upon desired packagefunctionality, additional sensors and/or other microelectroniccomponents may also be combined with the magnetometer and accelerometer.For example, a three axis MEMS gyroscope may further be combined withthe three axis accelerometer and magnetometer to produce amicroelectronic package, such as an Inertial Measurement Unit (IMU),having nine Degrees-of-Freedom (DOF).

BRIEF DESCRIPTION OF THE DRAWINGS

At least one example of the present invention will hereinafter bedescribed in conjunction with the following figures, wherein likenumerals denote like elements, and:

FIG. 1 is a planform or top-down view of an accelerometer wafer, whichincludes an array of non-singulated accelerometer die and which may beprocessed in accordance with a first exemplary embodiment of themicroelectronic package fabrication method;

FIG. 2 is a top-down view of a magnetometer wafer, which may positionedover and bonded to the accelerometer wafer shown in FIG. 1 to yield awafer stack during performance of the exemplary microelectronic packagefabrication method;

FIG. 3 is a cross-sectional view of a region of the wafer stack shown inFIG. 2, which encompasses a magnetometer die and an underlyingaccelerometer die and which may be processed to produce a multi-sensormicroelectronic package in parallel with a number of othermicroelectronic packages during the fabrication method;

FIGS. 4-8 are cross-sectional views of the microelectronic package shownin FIG. 3, as illustrated in at various stages of completion andfabricated in accordance with the first exemplary fabrication method;and

FIGS. 9 and 10 are cross-sectional views of a microelectronic package asillustrated in at various stages of completion and fabricated inaccordance with a further exemplary embodiment of the microelectronicpackage fabrication method.

For simplicity and clarity of illustration, the drawing figuresillustrate the general manner of construction, and descriptions anddetails of well-known features and techniques may be omitted to avoidunnecessarily obscuring the exemplary and non-limiting embodiments ofthe invention described in the subsequent Detailed Description. Itshould further be understood that features or elements appearing in theaccompanying figures are not necessarily drawn to scale unless otherwisestated. For example, the dimensions of certain elements or regions inthe figures may be exaggerated relative to other elements or regions toimprove understanding of embodiments of the invention.

DETAILED DESCRIPTION

The following Detailed Description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Any implementation described herein as exemplary is notnecessarily to be construed as preferred or advantageous over otherimplementations. Furthermore, there is no intention to be bound by anytheory presented in the preceding Background or the following DetailedDescription.

Terms such as “first,” “second,” “third,” “fourth,” and the like, ifappearing in the description and the subsequent claims, may be utilizedto distinguish between similar elements and are not necessarily used toindicate a particular sequential or chronological order. It will thus beunderstood that such terms may be used interchangeably and thatembodiments of the invention are capable of operation in sequences otherthan those illustrated or otherwise described herein. Furthermore, termssuch as “comprise,” “include,” “have,” and the like are intended tocover non-exclusive inclusions, such that a process, method, article, orapparatus that comprises a list of elements is not necessarily limitedto those elements, but may include other elements not expressly listedor inherent to such process, method, article, or apparatus. The term“coupled,” as appearing herein, is defined as directly or indirectlyconnected in an electrical or non-electrical manner. Furthermore, theterms “substantial” and “substantially” are utilized to indicate that aparticular feature or condition is sufficient to accomplish a statedpurpose in a practical manner and that minor imperfections orvariations, if any, are not significant for the stated purpose.

As appearing herein, the term “microelectronic component” is utilized ina broad sense to refer to an electronic device, element, or structureproduced on a relatively small scale and amenable to packaging in thebelow-described manner. Microelectronic components include, but are notlimited to, integrated circuits formed on semiconductor die, MEMSdevices, passive electronic components (e.g., a discrete resistor,capacitor, inductor, or diode), optical devices, and other small scaleelectronic devices capable of providing processing, memory, sensing,radiofrequency, optical, and actuator functionalities, to list but a fewexamples. The term “wafer” is utilized to encompass bulk semiconductor(e.g., silicon) wafers, layered structures (e.g., silicon-on-insulatorsubstrates), and other structures over which number of semiconductordevices, MEMS devices, or the like can be produced utilizing global orwafer-level processing techniques. The term “die” is utilized inreference to a singulated piece of a wafer on which one or moreintegrated circuits, MEMS devices, and/or another microelectroniccomponent has fabricated via wafer-level processing of the wafer.Finally, as still further appearing herein, the phrase “produced on,”the phrase “fabrication on,” and the like encompass the terms “over” and“in” such that a device “fabricated on” a semiconductor wafer may beproduced over a principal surface thereof, in the body of the wafer, ora combination thereof.

As indicated in the foregoing section entitled “BACKGROUND,”microelectronic packages are now commonly produced to contain amulti-axis accelerometer and a multi-axis magnetometer, which arecarried by an accelerometer die and a magnetometer die, respectively. Tooptimize the performance of such a microelectronic package, theaccelerometer die and the magnetometer die are ideally positioned suchthat sensing axes of the accelerometer are precisely aligned with thesensing axes of the magnetometer. It can be difficult, however, toensure precise alignment between the sensing axes of the accelerometerand magnetometer within exacting tolerances (e.g., tolerances on theorder of a few hundredths of a degree) utilizing conventionalfabrication methods. For example, even when carefully controlled, apick-and-place tool of the type conventionally utilized to position themagnetometer die relative to the accelerometer die during packagefabrication may only achieve rotational alignment tolerances of about1-2°. As a result, it may be necessary to thoroughly test the alignmentbetween the sensing axes of the magnetometer and accelerometer during orafter package fabrication; and to perform calibrations or otherwisecompensate for any detected misalignments between the sensing axes. Thisadds undesired cost, complexity, and time to the fabrication process.There thus exists a current industry demand to provide improvedmulti-sensor microelectronic package fabrication methods, which ensurehighly accurate alignment between the sensing axes of accelerometer andmagnetometer die on a repeatable and cost-effective basis.

The following describes embodiments of a method for producing amicroelectronic package containing an accelerometer die and amagnetometer die, which is positioned over and bonded to theaccelerometer die. Embodiments of the below-described fabrication methodare advantageously carried-out utilizing a wafer level stacking process,which enables highly precise alignment between the sensing axes of theaccelerometer and magnetometer die to be achieved on a repeatable basis.In at least some instances, rotational alignments between the sensingaxes within a few hundredths of a degree may be reliably achieved.Testing requirements to ensure alignment between the sensing axes andpost-fabrication calibration requirements may be greatly reduced, if notrendered unnecessary, as a result. The wafer stacking process alsoenables the sensing axes of numerous accelerometer and magnetometer diepairs to be aligned simultaneously, while the die remain in wafer formto improve manufacturing efficiency. As an additional benefit, themagnetometer die may be bonded directly to the accelerometer die duringperformance of the below-described fabrication method to form ahermetically-sealed cavity in which the accelerometer MEMS structure isenclosed. In this manner, the magnetometer die may be utilized to “cap”the accelerometer die thereby eliminating the need for a separate cappiece to reduce package size and cost. An exemplary embodiment ofmicroelectronic package fabrication process during which a magnetometerwafer is stacked onto an accelerometer wafer will now be described inconjunction with FIGS. 1-9.

Referring initially to FIG. 1, an exemplary accelerometer wafer 30 isschematically shown from a top-down or planform view. Accelerometerwafer 30 includes a frontside 31 over which a number of accelerometerdie 32 have been produced by wafer-level processing. At this juncture inthe fabrication process, accelerometer die 32 remain interconnected as asolid wafer and may consequently be referred to below as “non-singulatedaccelerometer die 32.” Accelerometer die 32 are spatially distributedacross wafer 30 in, for example, a grid arrangement. While a relativelylimited number of die 32 are shown in FIG. 1, any practical number ofaccelerometer die 32 can be distributed across wafer 30 in variousdifferent spatial arrangements. Accelerometer die 32 are interspersedwith a number of saw lanes 34, which are areas of wafer 30 lackingactive circuitry that are removed during singulation of wafer 30. Eachaccelerometer die 32 is produced to include a MEMS transducer structure36 and a number of bond pads 38, which are disposed over the frontsideof the die to provide points-of-contact to the circuitry formed thereon(not shown). MEMS transducer structure 36 may be located in a centralregion of each die 32, while bond pads 38 may be disposed in one or morerows bordering structure 36. It will be appreciated, however, that theillustrated layout is offered by way of example only and will varyamongst different embodiments.

FIG. 2 is a top-down view of a magnetometer wafer 40, which maypositioned over or stacked with accelerometer wafer 30 during anexemplary embodiment of the package fabrication method. When stacked inthis manner, magnetometer wafer 40 and accelerometer wafer 30 may becollectively referred to as “wafer stack 30, 40.” As shown in FIG. 2,magnetometer wafer 40 has been processed to include an array ofnon-singulated magnetometer die 42, which are distributed across thefrontside 41 of wafer 40. Magnetometer wafer 40 is produced to includethe same die number and the same general die arrangement asaccelerometer wafer 30 such that, when wafer 40 is stacked onto wafer30, each magnetometer die 42 overlies a different accelerometer die 32(FIG. 1), as described more fully below in conjunction with FIG. 3.Furthermore, as does accelerometer wafer 30, magnetometer wafer 40includes a number of saw lanes 44, which are interspersed withmagnetometer die 42. When magnetometer wafer 40 is stacked ontoaccelerometer wafer 30, saw lanes 44 of wafer 40 generally align withsaw lanes 34 of wafer 30 (FIG. 1) such that a common singulation processmay be utilized to separate wafer stack 30, 40 into individual pieces.

Magnetometer die 42 each include a solid state magnetometer 48 and anumber of bond pads 46, which provide points-of-contact tonon-illustrated circuitry formed on the frontside of die 42. Asindicated in FIG. 2, each magnetometer 48 may be formed on a centralportion of its corresponding die 42, while bond pads 46 may be arrangedin rows bordering magnetometer 48; however, again, this layout is merelyexemplary and will vary amongst embodiments. As further indicated inFIG. 2 by cross-hatching, die 42 may also include outer sacrificialregions 49 lacking active circuitry. When wafers 30 and 40 are stacked,sacrificial regions 49 may overlay and cover bond pads 38 (FIG. 1)provided on the underlying accelerometer die 32. Sacrificial regions 49may thus be removed after wafer stacking using, for example, asaw-to-reveal process to expose the bond pad shelves of accelerometerdie 32 on which bond pads 38 (FIG. 1) are disposed. This, in turn,allows aligning pairs of accelerometer die 32 and magnetometer die 42 tobe interconnected by wirebonding in the below-described manner. Thisnotwithstanding, magnetometer die 42 need not include sacrificialregions 49 in all embodiments, and other types of interconnections maybe utilized to interconnect corresponding pairs of die 32 and 42 infurther embodiments.

By the nature of their structure, magnetometer die tend to be morecompact than do accelerometer die; e.g., in many cases, a magnetometermay be one half or one third the size of a corresponding accelerometerdie. The spacing between magnetometer die 42 and/or the overall planformdimensions of each die 42 may thus be increased to ensure propervertical alignment between corresponding pairs of accelerometer die 32and magnetometer die 42 when wafers 30 and 40 are stacked in the mannershown in FIG. 2. This, in turn, may result in a slight decrease in theoverall device density of magnetometer wafer 40. However, any costpenalty associated with this decrease in magnetometer wafer density maybe more than offset by cost savings achieved by utilizing magnetometerdie 42 to cap accelerometer die 32 (instead of a separate cap piece) asdescribed below; and/or by eliminating or at least reducing testing andcalibration procedures that may otherwise required to ensure acceptablealignment between the sensing axes of die 32 and 42 (and, specifically,between the accelerometers and magnetometers carried thereby). A lowermagnetometer wafer density may also allow the planform dimensions ofmagnetometer die 42 to be increased potentially improving magnetometerperformance. Additionally, regions of magnetometer die 42 that remainunoccupied by magnetometer structures 48, bond pads 46, or theassociated circuitry may be utilized by, for example, fabricatingadditional control circuitry thereon or otherwise imparting this area ofdie 42 with a functionality useful in the package design.

FIG. 3 is a cross-sectional view taken through a relatively small regionof wafer stack 30, 40, which contains a single magnetometer die 42 andaccelerometer die 32 and which generally corresponds to dashed box 47identified in FIG. 2. Hereafter, the following description and theaccompanying figures will focus primarily on the manner in which theillustrated portion of wafer stack 30, 40 shown in FIG. 3 is processedto produce a single multi-sensor microelectronic package (identifiedhereafter by reference numeral “50”). Microelectronic package 50 isshown at various stages of completion in FIGS. 3-7 and in a completedstate in FIG. 8. As shown in FIGS. 3-8 and described below,microelectronic package 50 is provided by way of non-limiting exampleonly. It will be appreciated that various other types of microelectronicpackages can be produced utilizing embodiments of the below-describedmethod, which may include structural features and functionalities otherthan those of package 50. While the following description focusesprimarily on the processing of the relatively limited region of waferstack 30, 40 from which microelectronic package 50 is produced, it willbe understood that the below-described process steps will typically beperformed globally across wafer stack 30, 40 to produce a plurality ofmicroelectronic packages in parallel with microelectronic package 50,which may or may not be substantially identical to package 50.

During or after wafer stacking, magnetometer wafer 40 (FIGS. 2 and 3) isbonded to accelerometer wafer 30 (FIG. 1) at multiple locations suchthat each magnetometer die 42 is bonded to an underlying accelerometerdie 32. Each bonded pair of magnetometer die 42 and accelerometer die 32may be collectively referred to as “bonded sensor die stack 32, 42” or,more simply, “sensor die stack 32, 42” hereafter. With reference topartially-fabricated package 50 shown in FIG. 3, specifically,magnetometer die 42 is positioned over and bonded to accelerometer die32 to yield a bonded die stack 32, 42. In the illustrated example,magnetometer die 42 is bonded to accelerometer die 32 (and, moregenerally, magnetometer wafer 40 is bonded to accelerometer wafer 40) ina face-up orientation. Thus, indicated in FIG. 3, the non-active surfaceor backside 56 of magnetometer die 42 (and, therefore, the backside ofmagnetometer wafer 40) is bonded to the active surface or frontside 31of accelerometer die 32 (and, thus, the frontside of accelerometer wafer30). In further embodiments, magnetometer wafer 40 may be bonded toaccelerometer wafer 30 in an inverted or face-down orientation such thatthe respective frontsides 41 of magnetometer die 42 are bonded to thefrontsides 31 of the corresponding accelerometer die 32, as describedmore fully below in conjunction with FIGS. 9 and 10.

In some embodiments, magnetometer wafer 40 (FIGS. 2 and 3) is bonded toaccelerometer wafer 30 (FIG. 1) such that each magnetometer die 42 capsthe underlying accelerometer die 32 and, perhaps, forms ahermetically-sealed cavity therewith. In this regard, rings of bondingmaterial (referred to herein as “seal rings”) may be deposited betweenwafers 30 and 40 at selected locations circumscribing or extendingaround the MEMS transducer structures 36 formed on accelerometer wafer30. This may be more fully appreciated by referring to FIG. 3 whereinone such seal ring 52 has been deposited between magnetometer die 42 andaccelerometer die 32. While shown in cross-section, it will beappreciated that seal ring 52 forms a continuous 360° seal and may havea generally rectangular, square, circular, or other planform geometry.Seal ring 52 circumscribes MEMS transducer structure 36, as taken alongan axis orthogonal to the frontside 31 of accelerometer die 32 and wafer30. Seal ring 52 is deposited to a thickness sufficient to create avertical standoff or gap between backside 56 of magnetometer die 42 andfrontside 31 of accelerometer die 32. As a result, a hermetically-sealedcavity 58 is formed between the adjacent surface of magnetometer die 42and accelerometer die 32, is circumferentially bound by seal ring 52,and encloses MEMS transducer structure 36. Hermetically-sealed cavity 58contains a known pressure selected to optimize performance of MEMStransducer structure 36. In one embodiment, the pressure withinhermetically-sealed cavity 58 may be about 1 atmosphere (atm); however,the pressure within cavity 58 may be greater or less than 1 atm in otherembodiments.

Any material suitable for creating a hermetic or airtight seal andsuitable for attaching magnetometer die 42 to accelerometer die 32 canbe utilized to form seal ring 52 (and the other non-illustrated sealrings created across wafer stack 30, 40 shown in FIG. 2). Anon-exhaustive list of suitable bonding materials includesaluminum-germanium alloy, copper, and copper alloys. Such materials maybe deposited to form seal ring 52 and the other non-illustrated sealrings utilizing a plating process in an embodiment; however, otherdeposition methods can be utilized in further embodiments. Afterdeposition of seal rings 52 at the desired locations, a bonding processmay be performed during which die 32 and 42 (and, more generally, wafers30 and 40) are brought into contact and subject to heat treatment tomelt or soften the bonding material and thereby form the desired seals.The bonding process can be carried-out at a controlled pressure toimpart hermetically-sealed cavity 58 (FIG. 3) and the othernon-illustrated cavities with a desired internal pressure. The pressureat which the bonding process is carried-out may be greater than thedesired pressure within cavity 58 if the bonding process is performedunder elevated temperature conditions. To provide a non-limitingexample, if it is desired for the pressure within cavity 58 to beapproximately 1 atm, the bonding process may be carried-out at apressure of 2-4 atm and at an elevated temperature such that the desiredpressure is achieved within cavity 58 upon cooling of microelectronicpackage 50.

After bonding wafers 30 and 40, corresponding pairs of accelerometer die32 and magnetometer die 42 may be interconnected, singulated, andsubject to further processing to complete the multi-sensormicroelectronic packages. Notably, at this stage in the fabricationprocess, several benefits have already been achieved. First, precisealignment has been ensured between the sensing axes of die 32 and 42 byvirtue of the above-described wafer stacking and alignment process. Inmany cases, wafer stacking may allow alignment within 50 microns, which,over the span of a 100 millimeter planform dimension (as an example) maytranslate into an alignment accuracy of about 0.03°. Such alignmentaccuracies well-exceed those achievable by die-on-die placementutilizing a pick-and-place tool. Second, by directly bonding eachmagnetometer die 42 to its corresponding accelerometer die 32 tosealingly enclose MEMS transducer structure 36, the need for a separatecap piece is eliminated to reduce package size and fabrication costs.With these benefits achieved, the particular manner in whichaccelerometer die 32 and magnetometer die 42 are interconnected andpackaged during the latter stages of the manufacture method may be oflesser importance and will inevitably vary amongst differentembodiments. Nonetheless, for completeness, the following will describeone exemplary and non-limiting manner in which die stack 32, 42 shown inFIG. 3 (and the other die stacks 32, 42 produced across wafer stack 30,40 shown in FIG. 2) may be interconnected and packaged.

Turning to FIG. 4, a saw-to-reveal process may be carried-out to exposebond pads 38 of the non-singulated accelerometer die 32. During thesaw-to-reveal process, selected regions of magnetometer wafer 40 maynext be removed to reveal the underlying bond pads 38 of accelerometerdie 32. In one embodiment, the selected regions of wafer 40 are removedby forming a number of linear channels, slots, or grooves in wafer 40,as generally indicated in FIG. 3 by dashed lines 60. The channels areconveniently produced utilizing a dicing saw and extend alongsubstantially parallel axes entirely through the thickness ofmagnetometer wafer 40, but do not penetrate into the underlyingaccelerometer wafer 30; e.g., the channels may be formed assubstantially parallel saw lanes having a depth substantially equivalentto the magnetometer wafer thickness. The channels may extend entirelyacross magnetometer wafer 40 and, thus, effectively separate wafer 40into a number of elongated strips; however, this need not always be thecase. In the case of microelectronic package 50, specifically, theresulting structure is shown in FIG. 4. As can be seen, thesaw-to-reveal process has resulted in the removal of sacrificial regions49 of magnetometer wafer 40 (FIG. 3) thereby imparting die 42 withvertical sidewalls 64 and exposing bond pad rows 38 provided on the bondpad shelves of accelerometer die 32. If desired, one or more of thenewly-exposed bond pad rows 38 may now be wirebonded to bond pads 46 tointerconnect die 32 and 42. Alternatively, interconnection of die 32 and42 may be carried-out after singulation of wafer stack 30, 40.

Wafer stack 30, 40 may next be singulated to separate stack 30, 40 intoa number of discrete die stacks 32, 42 to be incorporated into differentmicroelectronic packages. FIGS. 6 and 7 illustrate partially-completedmicroelectronic package 50 including one such die stack 32, 42 producedby singulation of wafer stack 30, 40 (FIG. 2). As can be seen,singulation has imparted accelerometer die 32 with four substantiallyvertical sidewalls 66. Singulation also imparts magnetometer die 42 withtwo substantially vertical sidewalls 68 (identified in FIG. 6); theother two substantially vertical sidewalls 64 of die 42 previouslydefined during the above-described saw-to-reveal process. Singulation isconveniently carried-out utilizing a dicing saw, which is directedthrough wafer stack 30, 40 along overlapping saw lanes 34 and 44 (FIGS.1-2); however, other singulation techniques can be utilized to separatestack 30, 40 into discrete pieces including, for example, laser cuttingand scribing with punching. If not previously performed, wirebonding maynow be utilized to create a number of wire bonds 70 interconnectingmagnetometer bond pads 46 with corresponding accelerometer bond pads 38.No longer in wafer form, accelerometer die 32 and magnetometer die 42may be referred to hereafter as “singulated die.”

In certain implementations, the degrees of freedom attributed tomicroelectronic package 50 and the other microelectronic packagesproduced across wafer stack 30, 40 (FIG. 2) may be provided exclusivelyby die 32 and 42. Thus, in embodiments wherein the magnetometer andaccelerometer are both three axis devices, microelectronic package 50may have a total of six DOFs. Alternatively, one or more additionalsensors (and/or other microelectronic components) may be packaged withdie stack 32, 42 to impart the completed package 50 with additionalDOFs. For example, in further implementations, sensor die stack 32, 42may be further combined with a three axis gyroscope to yield a 9-DOFmicroelectronic package. Further illustrating this point, FIG. 7 depictsone manner in which sensor die stack 32, 42 may be further stacked ontoan Application Specific Integrated Circuit (ASIC) die 72, which has beenbonded over a gyroscope die 74. Gyroscope die 74 includes a MEMStransducer structure 76, which may be enclosed within ahermetically-sealed cavity 78 formed between gyroscope die 74 and ASICdie 72. As was previously the case with accelerometer cavity 58, a knownpressure may be contained within hermetically-sealed cavity 78. Ascavity 78 is fluidly isolated from cavity 58, the pressure withinhermetically-sealed cavity 78 may vary as compared to (and willtypically be significantly less than) the pressure withinhermetically-sealed cavity 58 and can be chosen to optimize performanceof MEMS gyroscope 76. Bond pads 80 are provided on bond shelf regions ofASIC die 72, which extend laterally beyond accelerometer die 32. Tointerconnect ASIC die 72 with accelerometer die 32 (and, therefore, alsomagnetometer die 42), wire bonds 82 may be formed between selectedaccelerometer bond pads 38 and ASIC bond pads 80. Wirebonding maylikewise be utilized to interconnect ASIC 72 and gyroscopic die 74 or,instead, the circuitry formed on ASIC die 72 may be electrically coupledto die 72 through a number of TSVs 84 formed through die 72. As furtherindicated in FIG. 7, a number of TSVs 86 may likewise be formed throughgyroscopic die 74 to provide signal communication from the frontside 88of die 74 to the backside 89 thereof. In further embodiments, sensor diestack 32, 42 may be positioned adjacent to die stack 72, 74 in aside-by-side relationship.

Conventional processing steps may now be performed to completefabrication of microelectronic package 50 and the other packagesproduced from wafer stack 30, 40. Further processing of package 50 mayentail encapsulation of die stack 32, 42 and any other componentspackaged therewith (e.g., die stack 72, 74 shown in FIG. 7) in a moldedpackage body. For example, a Fan-Out Wafer Level Packaging (“FO-WLP”)encapsulation process may be performed during which a pick-and-placetool is used to position partially-completed microelectronic package 50along with a number of other packages within the central opening of ataped mold frame. An encapsulant, such as a dielectric mold compound,may then be dispensed into the mold frame and over the array ofsemiconductor die. The encapsulant is thermally cured to produce amolded panel in which the array of semiconductor die is embedded, andthe taped mold frame may be removed to reveal the frontside of themolded panel through which the semiconductor die are exposed. A carriermay then be attached to the panel backside to allow a number of build-uplayers or Redistribution Layers (RDLs), as well as a BGA or othercontact array, to be formed over the panel frontside and the die exposedtherethrough. The RDL may include successively-deposited dielectriclayers in which a number of metal traces or interconnect lines areformed to provide electrically-conductive paths between the bond pads ofthe embedded die and the overlying BGA. Finally, the molded panel may besingulated to yield a number of microelectronic packages each containinga different encapsulated semiconductor die.

FIG. 8 illustrates microelectronic package 50 in a completed state afterperformance of a FO-WLP packaging process of the type described above.Die stack 32, 42 and die stack 72, 74 have been encapsulated within amolded package body 90 having a frontside 92. A number of RDLs 94 havebeen built-up over frontside 92 of package body 90. RDLs 94 are producedto include a network of interconnect lines 96 disposed within a body ofdielectric material 98. Interconnect lines 96 may comprise various metaltraces, vias, metal plugs, and/or the like, which collectively provideelectrically-conductive paths between the upper surface of frontsideRDLs 94 and through-silicon vias (TSVs) 86 (and, therefore, die 32, 42,72, and 74). Package body 98 may be formed as a number ofsuccessively-deposited (e.g., spun-on) dielectric layers, whileinterconnect lines 96 may be formed within body 98 utilizing well-knownlithographical patterning and conductive material (e.g., copper)deposition techniques; e.g., in one embodiment, each metal level may beproduced by patterning a mask layer deposited over a seed layer, platingexposed regions of the seed layer with copper or another metal, and thenremoving the mask layer to define the desired electrically-conductivefeatures. A contact array may be formed over RDLs 94 to provideexternally-accessible points-of-contact to interconnect lines 96 (and,therefore, signal communication to packaged die 32, 42, 72, and 74). Forexample, bumping may be performed to produce a BGA including a pluralityof solder balls 100 over the outermost RDLs 94 and in ohmic contact withinterconnect lines 96, as generally shown in FIG. 8.

The foregoing has thus provided an exemplary embodiment of amicroelectronic package fabrication method suitable for producing one ormore packages containing a magnetometer die positioned over and bondedto an accelerometer die. In the above-described embodiment, themagnetometer die was sealingly bonded to the accelerometer die and formtherewith a hermetically-sealed cavity enclosing a MEMS transducerstructure provided on the accelerometer die. By utilizing themagnetometer die to cap the accelerometer die in this manner, the needfor an additional cap piece can be eliminated thereby reducing packagesize and cost. Furthermore, the above-described wafer stacking andalignment process increases manufacturing efficiency and, moreimportantly, ensures precise alignment between the sensing axes beyondthat typically achievable utilizing a pick-and-place tool; e.g., incertain embodiments, alignments within few hundredths of a degree can beachieved. The ability to reliably attain such precision alignment mayeliminate or at least reduce post-fabrication testing requirements.

In the above-described exemplary embodiment, sensor die stack 32, 42 isincorporated a particular type of microelectronic package, namely,FO-WLP package 50 shown in FIG. 8. This example notwithstanding, it isemphasized that sensor die stack 32, 42 can be incorporated into variousdifferent types of package, including Chip Scale Packages (CSP packages)and other packages produced in accordance with Fan-In Wafer LevelPackaging (FI-WLP) approaches. Additionally, while the FO-WLP package 50was produce to include an Input/Out (I/O) structure in the form of oneor more redistribution layers and BGA, it will be appreciated thatvarious other I/O structures can be utilized in conjunction with theparticular package into which die stack 32, 42 is incorporated. Forexample, in embodiments wherein die stack 32, 42 is incorporated into aFI-WLP package, one or more redistribution layers, a leadframe, aninterposer, or the like may be utilized to provide signal communicationto die stack 32, 42 and any other microelectronic components containedwithin the package body. The particular contact array employed willlikewise vary in conjunction with the chosen I/O structure and canassume any form providing points-of-contact accessible from the exteriorof the microelectronic package. While, in the above-described exemplaryembodiment, the magnetometer wafer was bonded to the accelerometer waferin an face-up orientation, the magnetometer wafer may be bonded to theaccelerometer wafer in a face-down orientation such that the waferfrontsides are positioned adjacent one another. An exemplary embodimentof a multi-sensor package wherein magnetometer and accelerometer wafersare bonded in such a face-to-face or frontside-to-frontsideconfiguration is described below in conjunction with FIGS. 9 and 10.

FIGS. 9 and 10 are cross-sectional views of a microelectronic package110 shown in a partially-completed state and illustrated in accordancewith a further exemplary embodiment of the present invention. As waspreviously the case, microelectronic package 110 includes anaccelerometer die 112 and a magnetometer die 114, which is positionedover and bonded to accelerometer die 112. Accelerometer die 112includes, in turn, a frontside 116 over which a MEMS accelerometerstructure 118 and a number of bond pads 120 are disposed. Additionally,a number of TSVs 122 are formed in the body of accelerometer die 112.Magnetometer die 114 likewise includes a frontside 124 over which amagnetometer structure 126 and a number of bond pads 128 are formed.Magnetometer die 114 is advantageously bonded over accelerometer die112, while die 112 and 114 remain in wafer form. Thus, as indicated inFIG. 9, a magnetometer wafer 130 containing magnetometer die 114 (aswell as a number of other non-illustrated magnetometer die) may bepositioned and bonded over an accelerometer wafer 132 containingaccelerometer die 112 (as well as a number of other non-illustratedaccelerometer die) using a wafer level stacking process similar to thatdescribed above; e.g., bonding material rings 134 may be depositedbetween die 112 and 114 and around MEMS accelerometer structure 118 tocreate a hermetically-sealed cavity 136 enclosing structure 118.

In contrast to the exemplary embodiment described above in conjunctionwith FIGS. 1-8, magnetometer wafer 130 and accelerometer wafer 132 (and,more specifically, magnetometer die 114 and accelerometer die 112) arebonded in face-to-face configuration; that is, such that the frontside124 of die 114 is bonded directly to the frontside 116 of die 112. Inthis case, electrically-conductive bodies 138 may be deposited toelectrically interconnect bonds pads 128 provided on magnetometer die114 with corresponding bond pads 120 provided on accelerometer die 112.Furthermore, as may be appreciated by comparing FIG. 10 to FIG. 11,back-grinding, Chemical Mechanical Planarization (CMP), or anotherthinning process may be performed after bonding to bring wafers 130 and132 to a desired final thickness and expose TSVs 122 through thebackside of wafer 132 and accelerometer die 122. The wafer stack maythen be singulated to separate die stack 112, 114 shown in FIG. 10 fromthe other non-illustrated die stacks. Die stack 112, 114 may then becombined with additional sensors and/or other microelectroniccomponents, as appropriate to achieve the desired package functionality;e.g., as noted above, die stack 112, 114 may be combined with a threeaxis gyroscope to yield a 9-DOF microelectronic package. Additionalprocessing steps (e.g., encapsulation and formation of an I/O structure)may then be performed to complete fabrication of package 110 in theabove-described manner.

There has thus been provided multiple exemplary embodiments of afabrication method for producing a multi-sensor microelectronic package.In one embodiment, the method includes positioning a magnetometer wafercomprised of an array of non-singulated magnetometer die over anaccelerometer wafer comprised of an array of non-singulatedaccelerometer die. The magnetometer wafer is bonded to the accelerometerwafer to produce a bonded wafer stack. The bonded wafer stack is thensingulated to yield a plurality of multi-sensor microelectronic packageseach including a singulated magnetometer die bonded to a singulatedaccelerometer die.

In a further embodiment, the above-described fabrication method includesthe steps/processes of obtaining (whether by independent fabrication,purchase from a supplier, or otherwise) a magnetometer die and anaccelerometer die each having multiple sensing axes. The magnetometerdie is then positioned over an accelerometer die such that the sensingaxes of the magnetometer die align with the sensing axes of theaccelerometer die. The magnetometer die is preferably positioned overthe accelerometer die, while both die remain in non-singulated waferform utilizing a wafer stacking technique of the type described above;however, the possibility that positioning is performed after singulationof the magnetometer die and/or the accelerometer die in at least someembodiments is by no means precluded. The magnetometer die may be bondedto the accelerometer die such that a hermetically-sealed cavity iscreated enclosing a MEMS transducer structure formed on theaccelerometer die.

Embodiments of a multi-sensor microelectronic package have also beenprovided. In one embodiment, the microelectronic package includes asingulated accelerometer die having a MEMS transducer structure, asingulated magnetometer die positioned over the transducer structure,and a ring of bonding material. The ring of bonding material bonds thesingulated magnetometer die to the singulated accelerometer die suchthat a hermetically-sealed cavity is formed enclosing the transducerstructure.

While at least one exemplary embodiment has been presented in theforegoing Detailed Description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the foregoing Detailed Description willprovide those skilled in the art with a convenient road map forimplementing an exemplary embodiment of the invention. It beingunderstood that various changes may be made in the function andarrangement of elements described in an exemplary embodiment withoutdeparting from the scope of the invention as set-forth in the appendedclaims.

What is claimed is:
 1. A multi-sensor microelectronic package, comprising: a singulated accelerometer die comprising: a first Microelectromechanical Systems (MEMS) transducer structure; a bond pad shelf; and a first row of bond pads on the bond pad shelf; a singulated magnetometer die positioned over the first MEMS transducer structure; a ring of bonding material bonding the singulated magnetometer die to the singulated accelerometer die; and a first hermetically-sealed cavity formed between the singulated magnetometer and the singulated accelerometer die, circumferentially bounded by the ring of bonding material, and enclosing the first MEMS transducer structure.
 2. The multi-sensor microelectronic package of claim 1 wherein the singulated magnetometer die comprises: a frontside; a backside opposite the frontside; and a second MEMS transducer structure formed on the frontside and aligning with the first MEMS transducer structure, as taken along an axis orthogonal to the frontside.
 3. The multi-sensor microelectronic package of claim 1 wherein the singulated magnetometer die comprises: a backside; a second row of bond pads on the backside of the singulated magnetometer die and wirebonded to the first row of bond pads; and a sawn vertical sidewall located between the second row of bond pads and the first row of bond pads, as taken along an axis parallel to the backside.
 4. The multi-sensor microelectronic package of claim 3 further comprising an Application Specific Integrated Circuit (ASIC) die adjacent the singulated accelerometer die and having a third row of bond pads wirebonded to the second row of bond pads.
 5. The multi-sensor microelectronic package of claim 1 further comprising a gyroscope die interconnected with the singulated magnetometer die and with the singulated accelerometer die.
 6. The multi-sensor microelectronic package of claim 1 wherein the singulated magnetometer die comprises: a frontside; a backside opposite the frontside; and a second MEMS structure formed on the frontside and aligning with the first MEMS structure, as taken along an axis orthogonal to the frontside.
 7. The multi-sensor microelectronic package of claim 1 wherein the ring of bonding material is composed of an electrically-conductive material.
 8. A multi-sensor microelectronic package comprising: a singulated accelerometer die comprising a frontside on which a first Microelectromechanical Systems (MEMS) transducer structure is formed; a singulated magnetometer die positioned over the first MEMS transducer structure, the singulated magnetometer die comprising: a frontside; a backside opposite the frontside; and a second MEMS structure formed on the frontside of the singulated magnetometer die and aligning with the first MEMS structure, as taken along an axis orthogonal to the frontside; a ring of bonding material bonding the backside of the singulated magnetometer die directly to the frontside of the singulated accelerometer die; and a first hermetically-sealed cavity formed between the singulated magnetometer and the singulated accelerometer die, circumferentially bounded by the ring of bonding material, and enclosing the first MEMS transducer structure.
 9. The multi-sensor microelectronic package of claim 8 wherein the ring of bonding material is composed of an electrically-conductive material.
 10. The multi-sensor microelectronic package of claim 8 further comprising: a bond pad on the frontside of the singulated magnetometer die; and a through silicon via formed through the singulated accelerometer die and electrically coupled to the bond pad through the ring of bonding material.
 11. The multi-sensor microelectronic package of claim 8 wherein the singulated accelerometer die comprises: a bond pad shelf; and a first row of bond pads on the bond pad shelf.
 12. The multi-sensor microelectronic package of claim 11 wherein the singulated magnetometer die comprises: a backside; a second row of bond pads on the backside of the singulated magnetometer die and wirebonded to the first row of bond pads; and a sawn vertical sidewall located between the second row of bond pads and the first row of bond pads, as taken along an axis parallel to the backside.
 13. The multi-sensor microelectronic package of claim 12 further comprising an Application Specific Integrated Circuit (ASIC) die adjacent the singulated accelerometer die and having a third row of bond pads wirebonded to the second row of bond pads.
 14. The multi-sensor microelectronic package of claim 8 further comprising a gyroscope die interconnected with the singulated magnetometer die and with the singulated accelerometer die.
 15. The multi-sensor microelectronic package of claim 14 further comprising: an Application Specific Integrated Circuit (ASIC) die adjacent the singulated accelerometer die; and a second hermetically-sealed cavity formed between the gyroscopic die and the ASCI die; wherein the gyroscope die comprises a third MEMS transducer structure enclosed by the second hermetically-sealed cavity.
 16. A multi-sensor microelectronic package, comprising: a singulated accelerometer die having a frontside, a backside opposite the frontside, and a first Microelectromechanical Systems (MEMS) transducer structure formed on the frontside; a singulated magnetometer die having a frontside, a backside opposite the frontside, and a second MEMS transducer structure formed on the frontside; and bonding material bonding the backside of the singulated magnetometer die directly to the frontside of the singulated accelerometer die.
 17. The multi-sensor microelectronic package of claim 16 further comprising a first hermetically-sealed cavity formed between the singulated magnetometer die and the singulated accelerometer die, the first hermetically-sealed cavity enclosing the first MEMS transducer structure and containing a first internal pressure.
 18. The multi-sensor microelectronic package of claim 17 further comprising a gyroscope die disposed in a stacked relationship with the singulated accelerometer die and the singulated magnetometer die, the gyroscope die having a third MEMS transducer formed thereon.
 19. The multi-sensor microelectronic package of claim 18 further comprising: an Application Specific Integrated Circuit (ASIC) die disposed between the gyroscope die and the accelerometer die; and a second hermetically-sealed cavity formed between the ASIC die and the gyroscope die, the second hermetically-sealed cavity enclosing the third MEMS transducer structure and containing a second internal pressure less than the first internal pressure.
 20. The multi-sensor microelectronic package of claim 19 wherein the ASIC die comprises at least one bond shelf region extending laterally beyond the accelerometer die. 